Engine mid plate questions

3/8th is pretty meaty for a mid plate. I have a CE one for my small block that had spacers included with it , but at .125" I don't thing pilot engagement would be as much of an issue.
I'd suspect with a thicker plate / spacer , the spacer would register in the crank and be machined to locate the converter precisely , but I don't recall ever seeing this done.
Not much different that a conversion kit I think.